1. Field of the Invention
The present invention relates to a heat dissipation method and related apparatus, and more particularly, to a heat dissipation method and related apparatus capable of controlling heat dissipation based on temperatures measured at an intake vent and an outlet vent.
2. Description of the Prior Art
Projectors can display data such as images, texts or files on a screen and are thus widely used in events such as commercial exhibitions or educational trainings. In most projectors, images are generated by projecting light provided by a light source from the interior of the projectors. Since a light source creates heat during light emission, the internal temperatures at different location of a projector must be carefully controlled so that each device of the projector can function with its best efficiency and can have a longer lifetime. Normally, a fan is disposed near the light source for lowering the internal temperature of the projector. The rotational speed of the fan is controlled based on temperatures measured by a sensor. This control mechanism is well known to those skilled in the art and is referred to the V-T (Velocity-Temperature) operation.
Reference is made to FIG. 1 for a diagram illustrating a prior art method for controlling the V-T operation. In FIG. 1, the horizontal axis represents temperatures measured by the sensor, and the vertical axis represents the rotational speed of the fan. Generally speaking, the V-T operation is performed by controlling the rotational speed of the fan based on temperatures measured by the sensor. When the temperature measured by the sensor is not greater than a temperature Tmin, the rotational speed of the fan is set to a minimum value RPMmin. When the temperature measured by the sensor is between the temperature Tmin and a temperature Tmax, the rotational speed of the fan is proportional to the measured temperature. When the temperature measured by the sensor is greater than the temperature Tmax, the rotational speed of the fan is set to a maximum value RPMmax.
In a prior art projector, two sensors S1 and S2 are respectively disposed near an intake vent and an outlet vent of the projector. The recommended range of operational temperature for a projector is defined based on external temperature in the specification of the projector. Since the intake vent of the projector is near the external environment, a first temperature T1 measured by the sensor S1 can reflect temperature variations of the external environment. The prior art projector can thus control the V-T operation of the fan based on the first temperature T1. On the other hand, the function of the outlet vent is to provide a heat dissipation path for the projector. Therefore, a second temperature T2 measured by the sensor S2 can reflect temperature variations of the projector. When the projector remains idle for a certain period of time, its body temperature and the temperature of the external environment can be nearly identical. When the projector is under operation, the second temperature T2 will be larger than the first temperature T1.
Reference is made to FIG. 2 for a flowchart illustrating a prior art heat dissipation method for a projector. The flowchart in FIG. 2 includes the following steps:
Step 200: start.
Step 210: measure a first temperature T1 near the intake vent of the projector using a sensor S1.
Step 220: measure a second temperature T2 near the outlet vent of the projector using a sensor S2.
Step 230: control the V-T operation of the fan based on the first temperature T1.
Step 240: determine if the second temperature T2 is larger than a threshold temperature TTH; if second temperature T2 is larger than the threshold temperature TTH, execute step 250; if the second temperature T2 is not larger than the threshold temperature TTH, execute step 230.
Step 250: shut down the projector.
In FIG. 2, the threshold temperature TTH represents the maximum temperature allowable for the body of the projector. When the body temperature of the projector exceeds the threshold temperature TTH, the internal devices of the projector may fail to function normally, or suffer from permanent damages. The sensor S1 is used to measure the temperature variations of the external environment, and the sensor S2 can reflect whether the heat dissipation path of the projector is blocked. Under normal operations, the heat dissipation path of the projector is completely unobstructed. However, a user may dispose the projector near an impediment (such as a wall or another equipment) in a way that the heat dissipation path of the projector is blocked by the impediment. Based on the influence of the impediment on heat dissipation, the degree of the above-mentioned obstruction can be defined as full-blockage or partial-blockage. Full-blockage can take place when the user disposes the projector in close vicinity to the wall so that the heat dissipation path of the projector is completely blocked. Under these circumstances, the heat generated by the light source of the projector is almost entirely accumulated inside the projector, and the body temperature of the projector thus rises sharply. Once the second temperature T2 measured by the sensor S2 exceeds the threshold temperature TTH, the prior art method executes step 250 for shutting down the projector. Partial-blockage can take place when the outlet vent of the projector is near another equipment and only part of the heat dissipation path of the projector is obstructed. Therefore, some heat generated by the light source of the projector can still be dissipated outside the projector, and the body temperature of the projector only rises gradually. Under these circumstances, the prior art method controls the V-T operation of the fan based on the first temperature T1. If the fan dissipates heat with a speed slower than that of heat accumulation due to partial-blockage, the body temperature of the projector will continue to increase gradually. Once the second temperature T2 measured by the sensor S2 exceeds the threshold temperature TTH, the prior art method executes step 250 for shutting down the projector.
In the prior art method, the projector controls the V-T operation of the fan based on the first temperature T1 measured by the sensor S1 regardless of the temperature variations at the outlet vent. The ability of heat dissipation provided by the fan is entirely controlled based on the first temperature T1, and the second temperature T2 is only used for determining when to shut down the projector. Therefore, the prior art method cannot respond to body temperature variations due to heat accumulation. When the outlet vent of the projector is partially blocked, heat dissipation provided by the fan controlled by the first temperature T1 is not capable of responding to heat accumulation due to different degrees of partial-blockage. The prior art projector cannot dissipate the redundant heat in time. In addition, although the projector can still function when the second temperature T2 is smaller than the threshold temperature TTH, the body temperature of the projector will continue to increase gradually as a result of heat accumulation caused by partial-blockage, The internal devices or plastic material can be placed in an environment having a temperature outside the best operating temperature range, which may cause damages and deformation to the internal devices and plastic material.